PDA Virus / Worm / Trojan / Spyware

Please be gentle if this has been covered elsewhere. It probably has, but my creativity for searching does not go beyond "Axim" or "PDA" matched with the above, and I get no hits.

My question is about Dell Axim PDAs (X50V with Windows Mobile 2003 Second Edition operating system) and how concerned I need be about getting one of the above nasties. I do not see any firewalls on my new unit (it's my first PDA, so I have a big learning curve). My PC is protected, but my concern is for when the PDA connects to the internet. I do not want it to get something that either affects it or is subsequently transferred to my PC.

Are there links somewhere of good reading on this or any advice? I do not know how believable the companies' websites are that sell such products as to the susceptibility of the PDA. I figured that this forum would be the best to get an impartial intelligent answser.

Thanks,
Dobermann